Source: http://io9.com/why-are-you-still-washing...

“[U]nless you have a really good reason for washing in warm or hot, such as really stinky clothes or cloth diapers, go for cold. It saves energy, and your clothes will last longer.”

Indeed, cold water is actually good for certain clothes. Lower temperatures protect the dyes, and therefore the color of clothes, while also helping to preserve the fit of the clothes by preventing shrinkage, particularly along the seams. What’s more, some stains, like blood, should only be washed in cold water. Warm water just makes blood stains set in.

So aside from some rare instances, there’s really no reason for you to keep washing your clothes in warm water. The Laundry Goddess offers some practical tips:

Personally, I have found that you can wash everything in cold water successfully, as long as you follow a few basic rules: Only use liquid detergent, as most powders need warm water to completely dissolve and clean successfully. Use the proper amount of detergent – too little and your wash load will not come clean, and too much will leave a soapy residue behind on your wash.

Also, do not overload the washer; be sure to leave room for items to move around in the water.